New guy on the Vortex, and just wanted to say thanks!
This is just me leaving a big THANK YOU to TopDownTony and the rest of you lot for the excellent photos and advice on fixing exactly what my problem turned out to be. With summer approaching, having my AC stuck blowing hot air was not going to be an option.
Now, I don't know about the rest of you, but in my 2000 GTI, even with Tony's excellent directions, getting in there to see what he'd photographed was tough. I tried lying on my back with the passenger seat laid-back, hanging half-in-half-out of the car... all sorts of things. Granted, not nearly as tough as tearing my dash apart to figure out what turned out to be a simple fix, but still pretty tough for a non-contortionist.
What I found to work really well was to use my smartphone's camera with flash to snap a few photos of the area back in there, so I could "visualize" what I was feeling with my hands. The problem area is very easy to reach -- just not see with your eyes. Using the camera made it real easy to find the tube that the lever had fallen out of, etc.
Anyway, huge THANKS again to @TopDownTony and the rest of you who've chimed in. Saved me LOADS of time and frustration. God I love the Internet.